22 research outputs found
Lower hybrid current drive at high densities of ITER
As widely documented by available experimental and modelling data [1,2], a broadening
in the lower hybrid (LH) wave frequency and n_// (parallel wavenumber) spectrum is
produced by parametric instability (PI) that can affect the propagation and deposition of
the LH power launched in tokamak plasmas. The electronic dynamics at the plasma edge
mainly determines the occurrence of the ion-sound quasimode-driven PI, whose growth
rate is intrinsically high at the radial layers close to the antenna-plasma interface, as its
maximum occurs in the same conditions necessary for performing the antenna coupling
(i.e.: Ï_peâÏ_0 â„1 at the plasma edge). The radial extent in the plasma of the region with
high growth rate determines the spectral broadening size. Radially deeper is this region,
smaller are the convective losses and consequently bigger is the spectral broadening. The
present work shows that considering a case of relatively high densities (n_e) and low
electron temperatures (T_e) of the scrape-off layer (SOL), the LH spectral broadening
should be strong enough to produce the radiofrequency (RF) power deposition at the very
plasma periphery of ITER (International Thermonuclear Experiment Reactor).
Conversely, operating with slightly low ne and high T_e in the SOL, the radial extent of the
PI region results reduced and, consequently, a useful LHCD can be performed in the
plasma bulk